What is the difference between PC2-4200 (DDR2-533), PC2-5300 (DDR2-667), PC2-6400 (DDR2-800), and PC2-8500 (DDR2-1066)?
PC2-4200 (DDR2-533), PC2-5300 (DDR2-667), PC2-6400 (DDR2-800), and PC2-8500 (DDR2-1066) memory are all types of Double Data Rate, second-generation SDRAM, usually referred to as DDR2. The varying numbers refer to the different speeds of memory your computer was designed for.
Let’s take a look at PC2-4200 (DDR2-533) to break it down simply.
PC2-4200 (DDR2-533) refers to the bandwidth of the memory. A PC2-4200 module has the bandwidth of 4.2 GB/sec; therefore, it is referred to as PC2-4200.
DDR2-533 refers to the effective front-side bus speed of your system. While your DDR2 system or motherboard may operate a 266MHz front-side bus, its effective front-side bus speed is 533MHz because DDR2 effectively doubles the amount of data transferred per cycle that a non-DDR2 system would.
The same holds true for PC2-5300 (DDR2-667), which has a bandwidth of 5.3GB/sec and is designed for use in systems and motherboards that require a 333MHz front-side bus, with an effective front-side bus speed of 667MHz. And the same holds true for PC2-6400 (DDR2-800), which has a bandwidth of 6.4GB/sec and is designed for use in systems and motherboards that require a 400MHz front-side bus, with an effective front-side bus speed of 800MHz.
Though DDR2 memory was designed to be backward-compatible (meaning you can use PC2-5300 module in a computer designed to use PC2-4200, or vice-versa)
